Balloon dilatation catheter apparatuses for a variety of medical applications, such as percutaneous transluminal coronary angioplasty (PTCA), are well known in the art. The use and construction of such balloon catheters is well known in the medical art, as generally described for example in U.S. Pat. Nos. Re. 32,983 (Levy) and 4,820,349 (Saab). Other patents generally showing the application of various types of balloon catheters include U.S. Pat. Nos. 4,540,404 (Wolvek), 4,422,447 (Schiff), and 4,681,092 (Cho, et al.).
It is also well known in the medical art to employ catheters having shafts formed with a plurality of lumens in instances where it is necessary or desirable to access the distal end of the catheter or a particular internal body location simultaneously through two or more physically separate passageways. For example, U.S. Pat. No. 4,576,772 (Carpenter) is directed to increasing the flexibility or articulatability of a catheter having a shaft formed with a plurality of lumens that provide distinct conduits for articulating wires, glass fiber bundles, irrigation, and vacuum means.
It is also known, as shown in U.S. Pat. Nos. 4,299,226 (Banka) and 4,869,263 (Segal et al.), to employ multi-lumen catheters with a balloon. The Banka patent shows a double-lumen catheter shaft of coaxial construction wherein the outer lumen carries saline solution to inflate a balloon, and an inner lumen, located coaxially inside the outer lumen, is adapted to receive a stylet or guide wire. In the Banka patent, the double-lumen dilatation catheter is designed to be coaxially contained within the single lumen of a larger diameter guide catheter. The Segal et al. patent shows a more complex dilatation catheter apparatus having five separate, non-coaxial lumens (FIGS. 1 and 2 of that patent) extending through the catheter, including a balloon inflation lumen 18, a distal lumen 17, a wire lumen 22, a pulmonary artery lumen 26, and a right ventricular lumen 28. Lumens 17 and 18 extend the entire length of the catheter from the proximal extremity to the distal extremity. Lumen 17 exists through the distal extremity 14b of the catheter. The distal extremity of lumen 18 is in communication with the interior of balloon 16 to permit inflation and deflation. Lumens 22, 26 and 28, on the other hand, only pass partly or completely through the larger diameter, proximal portion 14a of the catheter. The Segal et al. catheter apparatus is prepared by extrusion (col. 2, lines 53 and 54).
Multi-lumen catheters in conjunction with a balloon or inflatable element have also been adapted for a variety of special usages. U.S. Pat. Nos. 4,994,033 (Shockey et al.) and 5,049,132 (Shaffer et al.) are both directed to balloon catheters adapted for intravascular drug delivery. Both of these patents employ a similar concentric, coaxial, double balloon construction surrounding a central lumen. The larger, outer balloons in both cases include a set of apertures for the delivery of medication to surrounding tissue when the catheter is in place.
U.S. Pat. No. 4,681,564 (Landreneau) teaches another type of multi-lumen catheter in conjunction with a balloon element. In this patent, a first fluid passage is in communication with the balloon element so as to selectively inflate or deflate it; a second, separate fluid passage has outlet openings at its distal end for purposes of delivering medication or other treating fluid to the body space; and, a third, separate passage has drain openings communicating with the body space so as to drain excess fluids.
U.S. Pat. Nos. 4,581,017 (Sahota) and 5,108,370 (Walinsky) are both directed to perfusion balloon catheters designed to maintain blood flow through a blood vessel during a dilatation procedure, for example an angioplasty. In Sahota, a hollow, central shaft passes through the interior of the balloon element, and apertures in the side wall of the catheter shaft upstream and downstream from the balloon permit blood to flow into the shaft, past the balloon, and back into the blood vessel. A small, separate tube connected to the balloon is used to inflate and deflate the balloon. A generally similar balloon catheter construction is described in Walinsky.
For many balloon dilatation catheter applications, it is desirable to provide an elongated catheter shaft having varying degrees of stiffness along its length. For example, it is generally desirable to have a relatively stiff proximal shaft portion in order to transmit the necessary forces, particularly torque or axial forces, for advancing the catheter along a guide wire inside a body passageway for purposes of siting the balloon element at a selected internal location. At the same time, a more flexible "waist" or middle shaft portion can facilitate maneuvering the distal end of the catheter around turns and convolutions in the inner portions of the passageway. Various approaches to fabricating a workable variable stiffness balloon catheter have been described in the art.
U.S. Pat. No. 4,976,690 (Solar et al.) teaches one type of variable stiffness angioplasty catheter. In Solar et al., a "waist" portion, located between the balloon and the stiffer proximal end, is designed to have less stiffness and a correspondingly greater degree of flexibility. Such a catheter is intended to be utilized as part of a matched set, each having a different length of the less-stiff "waist" portion, to accommodate the needs of a particular patient (col. 2, lines 32-35). In one embodiment (FIGS. 2A and 2B), the less-stiff waist portion, 14 and 14' respectively, of the Solar et al. catheter is formed by extending the proximal neck of the balloon element, which is fabricated from a less-stiff material, to form a tubing section 30 that mates with and is bonded to a reduced-neck portion 27 at the distal end of the outer tube 25. In another embodiment (FIGS. 4A and 4B), the less-stiff waist portion 14 and 14' respectively, of the Solar et al. catheter is formed by necking down the wall thickness of outer tube 55. In still another embodiment (FIGS. 5A and 5B), "the variable stiffness of the waist portion 14, 14' is provided by varying the wall thickness and stiffness of the inner tube of the catheter," (col. 5, lines 57-59). In yet another embodiment of Solar et al. (FIGS. 6A and 6B), a double-lumen tubing construction is utilized in conjunction with the general technique of FIGS. 2A and 2B to obtain variable stiffness properties.
U.S. Pat. No. 5,085,649 (Flynn) teaches a very different approach to variable stiffness tubing. The Flynn tubing generally comprises an inner tubular layer of two co-tapered resins and a relatively hard, concentric outer shell. The hardness of the inner resin layer exceeds that of the outer resin layer, as does the hardness of the outer shell. In effect, this construction sandwiches a relatively softer, tapered center layer between harder inner and outer layers to obtain a torque-controlled tubing.
None of these prior art patents, which are incorporated herein by reference, however, is entirely satisfactory when applied to balloon dilatation catheters. The tapered-layer tubing of the Flynn patent would be difficult if not impossible to produce, especially for extremely long, very-thin-walled, small diameter catheter tubing required for such applications as PTCA catheters. In any event, because of the tapered construction, stiffness along the length of the Flynn tubing varies constantly and uniformly. Thus, the Flynn technique cannot be used to create discrete sections of tubing, each halving its own, substantially uniform stiffness, or to fabricate tubing having sharp disjunctions in stiffness along its length.
Although the Solar et al. patent is specifically directed to balloon catheters, it too has inherent limitations. First, the various Solar et al. techniques only provide for two sections having different degrees of stiffness along the catheter. For some applications, however, it is desirable to provide more than two different stiffnesses along the catheter. Second, for the embodiments of FIGS. 2A, 2B, 4A, 4B and 6A, 6B of Solar et al., the range of stiffness and related properties that can be achieved along the "waist" portion of the catheter is severely restricted because of the fact that the waist portion necessarily comprises the same material as the balloon member 12. Similarly, for the embodiments of FIGS. 5A, 5B of Solar et al., there are limitations imposed by the fact that the waist portion necessarily comprises the same material as the inner tube 61. Because catheters for use in such procedures as angioplasties must be of very small overall diameter, there is an extremely limited range of acceptable sidewall thicknesses. Therefore, having to rely on differences in sidewall thickness, or on a limited range of materials, in order to achieve a variable stiffness balloon catheter unduly restricts the design of these instruments.
These and other problems with and limitations of the prior art balloon catheters are overcome with the variable stiffness balloon catheters of this invention.